1. Technical Field
The present invention relates to an image display device and an image display method, and more specifically, to a technique suitable for the image display device having a display panel with a large variation in characteristics due to a variation in temperature.
2. Related Art
In the past, in an image display device for displaying a variety of information as an image, the image display device having a memory type display panel was practically used. Since the memory type display panel consumes an electric power only during a rewriting operation, the power consumption is very small as compared with a general display panel. Therefore, since an apparatus having the image display device can be reduced in size by reducing a battery capacity, the memory type display panel comes into the spotlight as a display panel suitable for apparatuses such as an electronic book.
An example of the memory type display panel is a display panel using a cholesteric liquid crystal as a display material. When the cholesteric liquid crystal is used, it is possible to achieve a high-rate rewriting operation of an image by a DDS (Dynamic Drive Scheme) driving system as a driving system with a cholesteric liquid crystal disclosed in U.S. Pat. No. 5,748,277.
However, although the display material of the display panel having the memory characteristic has the advantage as mentioned above, there is a problem that a viscosity is likely to vary depending on a temperature. For this reason, the temperature compensating process should be normally performed. That is, for the temperature compensating process, a period applying the driving voltage pulse or applied voltage values and so on should be varied based on the measured temperature of the display material. In particular, when the cholesteric liquid crystal is driven by applying DDS driving system, it is necessary that the temperature compensating process should be performed in a step where temperature difference of 1° C. or less is a prescribed width. In particular, it is required that the temperature compensating process is strictly performed when a gradation display is realized by plural levels.
Meanwhile, when the temperature of the display material is measured, the temperature is measured via members (glass, plastic, etc.) interposing the display material. Therefore, it occurs that the temperature at measuring point is different from the temperature of the display panel itself. In particular, when an ambient temperature of the display panel is varied as time goes on, a lot of time deviation occurs until the temperature of the display material reaches the measured temperature. Therefore, the temperature difference occurs between the measured temperature and the temperature of the display material at time of actual driving. In particular, the temperature difference is great when the environmental temperature of the display panel is rapidly varied, for example when the display panel is moved from the cold outdoors to the warm indoors. Therefore, there is a problem that the temperature compensating process cannot be sufficiently performed only on the base of values of the measured temperature.